Checking and adjusting pull-down device: VW (PD)

Special tools, testers and auxiliary items

Vacuum tester V.A.G 1368
Hand vacuum pump V.A.G 1390
Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
Adapter set V.A.G 1594
Chilling spray (commercially available)

Check function

Remove air intake elbow and plug vacuum hose of carburetor lower section/thermostat.
Start engine and run at idling speed.
Close air flap by hand. If air flap can be closed easily to a gap of
approx. 3 mm
and then greater resistance is felt, pull-down device is OK. If air flap can be closed completely without resistance, either diaphragm is torn or vacuum system is leaky.

Checking pull-down unit for leaks

Pull vacuum hose -1- of pull-down unit -2- off carburetor and connect vacuum tester V.A.G 1368 and hand vacuum pump V.A.G 1390.
Pull hose -3- off thermo time valve -4- and plug -arrow-.
Set tester to through-flow.
Use hand vacuum pump to create a vacuum of approx. 300 mbar.
Set tester so that vacuum is held on pull-down unit side.

Set vacuum on tester to 200 mbar. Vacuum set must not drop within 2 minutes; renew pull-down unit if necessary.

Checking and adjusting choke valve gap

Pull vacuum hose -1- of pull-down unit -2- off carburetor and connect vacuum tester V.A.G 1368 and hand vacuum pump V.A.G 1390.
Remove starter cover.

Operate throttle valve and turn fast idle cam -1- of cold starting device so that adjustment screw -2- is positioned on highest step of fast idle cam.

1st stage

Pull vacuum hose -1- off thermo time valve -2- (do not plug hose).
Set tester to through-flow and generate vacuum until air flap remains in one position.

Check gap with twist drill -3- at point indicated,
Specification: 1.2±0.2 mm
and adjust with Allen screw -4- if necessary.

Note:

Pump after each adjustment if necessary.

2nd stage

Plug vacuum hose -1-.
Use hand vacuum pump to create a vacuum of approx. 500 mbar.
Check gap,
Specification: 3.5±0.2 mm
and adjust with adjustment screw -5- if necessary.

Checking thermo time valve

Check function

Remove thermo time valve -1- and connect auxiliary hose -2- (for suction) and auxiliary wires from V.A.G 1594 (for connecting to battery).
Cool thermo time valve to below 0°C with commercially available cold spray.
Check through-flow of thermo time valve.
Specification: valve open
Connect auxiliary wires to battery. After 1 - 6 seconds the valve must close.

Checking resistance

Test conditions

Temperature of thermo time valve 20 - 30°C

Measure resistance between contacts of thermo time valve with multimeter.
Specification: 1.87 - 2.7ω